The known background regarding the state of the art in the matter of residual water treatment especially applied for residential houses, refers to systems that involve in their process train septic pits with airy systems, for the most part of the activated mud type, and airy packed zones oriented basically towards elimination of organic matter.
This invention, differing from treatment plants that it is common to find on the market, combines a high rate anaerobic digestion zone by means of two anaerobic filter chambers, followed by a packed aerobic zone, made up of more than two compartments in series, which allow for air conditioning extension in order to carry out nitrification. The treatment plant compartments are designed in such a way as to permit an adequate distribution of the water through the treatment train, diminishing considerably the inactive zones inside the treatment tanks. All compartments are integrated into a compact design that requires little space for its location and facilitates its operation and maintenance.
In order to support the innovative aspects of this invention, we have identified some treatment microplants offered on the market, which may or may not be protected by a patent. FIG. 1 presents the features of these treatment plants, and they are compared to the treatment plant subject matter of this patent application. The information concerning these treatment plants was extracted from their commercial catalogues.
The following Table 1 indicates the patents that were found as background and in force within the state of the art, such as was revealed in a search for the state of the art of U.S. patents.
TABLE 1 U.S. PATENT REFERENCES U.S. PAT. NO. INVENTOR DATE TITLE U.S. PAT. NO. Mullerheim March 4, Filtration System for 4191647 Williams 1980 Home Drainage U.S. PAT. NO. Colwell March 17, "In Situ" Residual 4251359 Freeman 1981 Water Treatment System U.S. PAT. NO. Laak Aug. 14, Drainage System for 4465594 1984 Segregated Residual Water Treatment U.S. PAT. NO. Ueda Aug. 31, Residual Water 5240597 1993 Treatment Equitment U.S. PAT. NO. Kuwashima Aug. 30, Method and Apparatus 5342523 1994 to Purify Tap Water U.S. PAT. NO. Kallenbach July 9, Method and Apparatus 5534147 Buchanan 1996 to Purify Wastes Gooddrich Skinner Poncelet Kallenbach
FIG. 1 shows that the great majority of treatment plants have an area for receiving crude sewage residual water inside what is considered the treatment plant in itself, under the framework of a compact design in which a single tank involves the various phases of treatment. In this sense, the plants corresponding to numbers 3, 5 and 10 in FIG. 1 specify a residual water receiving tank or conventional septic pits as a unit extra to what is in itself the package plant for water treatment, which is also a specification of the plant herein described.
No plant, except for plant 3 (FIG. 1), has a treatment zone based on a high-rate anaerobic reactor such as the anaerobic filter. Plant number 3 bases residual water treatment only on an anaerobic treatment, which limits its pollutant removal efficacy. Differently from the other treatment plants, this invention has 2 zones in series, based on anaerobic filters, which provide greater capability to absorb organic crests and limit biological mud production.
On the other hand, it is also possible to observe that most plants base water treatment on aerobic processes only, such as the activated mud, the percolator filter and the submerged filter. Differently from these plants, the plant subject matter of this invention bases its treatment on the combination of high-rate anaerobic and aerobic processes (2 anaerobic filters followed by at least 2 aerated, submerged-filter type zones). These provide versatility for adaptation of the microplant to fluctuating conditions in organic matter concentration, type of pollutants and residual water discharges. These conditions are frequently found in the in situ treatment of residual waters with small flows.
Water recirculation between the aerobic and anaerobic zones in the microplant permits to carry out the partial elimination of nitrogen from water by means of nitrification and denitrification. Plant 6 of FIG. 1 performs nitrification and denitrification, but by means of a completely mixed system of lot operation. The other treatment plants do not report in their respective documents the capability to denitrify, and only some nitrify, which implies ammonia nitrogen oxidation but not elimination of nitrogen from the water.
Plants number 7 and 12 in FIG. 1 effect water and sedimented mud recirculation up to the crude sewage water receipt zone by means of pumps in the first case and an "airlift" system in the second, with the intention of storing and treating the mud. In these arrangements, the substrate-microorganism interaction in a septic pit is poor; therefore, no high yields are accomplished in denitrification. Differently from these plants, the microplant subject matter of this invention establishes a water recirculation current, preferably by means of the "airlift" system, from the aerobic to the anaerobic zone. In these conditions, high-rate anaerobic reactors (2 anaerobic filters) possess adequate substrate-microorganism, which favors the process of denitrification and elimination of suspended and soluble organic matter.
On the other hand, we are mentioning as follows some U.S. patents related to residual water treatment for residential houses, which comprise the years from 1980 until 1996.
U.S. Pat. No. 4,191,647 (1980) refers to a residual water treatment system for in situ treatment in residential houses, which is composed of a filtration unit based on paper and vacuum suction. This separates the solid material from the liquid in the residual water, where the liquid is treated with chemical oxidizers for its further disposal and treatment in the soil, whereas the solids separated from the water and the filtering paper are submitted to a composting process. This treatment system requires area, chemical reagents, a vacuum system, and for the soil to be capable of eliminating the unloaded pollutants. This treatment plan goes a great distance beyond what is expounded in the treatment microplant subject matter of this invention, because the microplant presents a compact design, is based on biological treatment, and promotes the elimination of nitrogen. Besides, digestion of the mud generated is carried out, for the most part, in the treatment microplant.
U.S. Pat. No. 4,251,359 (1981) describes a residual water treatment system based on a conventional septic pit and a sand filter. The treatment system removes suspended material in the septic pit, basically, and dissolved and colloidal organic matter in the sand filter. Both units are in separate tanks. On the other hand, with respect to nitrogen removal, a possible nitrification process inside the filter is mentioned, which implies only oxidation of the ammonia nitrogen but not its elimination as molecular nitrogen. The differences between this patent and the treatment microplant subject matter of this invention, basically, are focused on the treatment process, compact design, and nitrogen elimination capability possessed by the microplant and not the process indicated in the patent.
U.S. Pat. No. 4,465,594 (1984) protects a residual water treatment system for residential houses, which comprises separation of "black" sewage residual waters from "gray" waters. Sewage residual waters go through a retention tank that acts as a septic pit, which is followed by a filter with a base of sand and stones placed on alternate layers inside the filter. The purpose of this is to eliminate organic matter and nitrify. The filter is aerated. The effluent treated water from the filter is mixed with the "gray" water, which previously went through a retention tank. The mixture is deposited in a tank so that the denitrification process will take place. The organic matter necessary for this process is provided by the "gray" water. Differently from this patent, the treatment microplant subject matter of this invention treats in a single compact-design tank the gray and black unloadings from the residential house.
U.S. Pat. No. 5,240,597 (1993) describes a semicompact residual water treatment system for residential houses, involving an anaerobic decomposition phase of the organic matter in a septic pit type compartment, as well as three aerated compartments that work according to the principles of the activated mud system. In the septic pit compartment there is a bomb submerged, whose function is to stir the medium, and certain amounts of fluorine are added, so that, as the patent claims, the solid degradation rate in the septic pit will be increased. In the aerobic zone, the distribution of air is performed by means of a blower and dispersers with different geometry, which in turn are capable of retaining biomass on their surface. A secondary sedimentator and a disinfection unit are specified within the water treatment train, but in separate tanks.
Contrary to the treatment microplant subject matter of this invention, this system does not have the conjunction of the elements of the process train in a single tank. Therefore, it is a semicompact system. Besides, it does not possess nitrogen elimination capability. The aerobic treatment system is based on the activated mud system and not on the series of aerobic submerged filters. For this, there are the ascending and descending alternate flows possessed by the microplant.
U.S. Pat. No. 5,342,523 patent (1994) describes a residual water treatment system for residential houses, consisting of 4 tanks, where the first two (separator tanks) are in parallel and the next two are in series. The parallel separating tanks may be operated alternately (every 6 months), so that only one tank works at a time and until it has become saturated with sedimented and floating mud. When this happens, the residual water begins entering the other separating tank (in parallel) through valves for deviating the residual water. The separator tank, which was saturated with mud, undergoes an air injection until accomplishing complete digestion of the mud. Parallel separator tanks function as conventional septic pits during water income, and as aerobic digesters of mud when the water does not return to the separator tanks. Both separator tanks in parallel are connected to a digestion tube, where the water, arising from any of the two parallel tanks (the one that is in operation), is treated aerobically. Afterwards, the water enters the last tank for its disinfecting.
This patent outlines a half batch type treatment of the residual water, where the residual water is treated continuously and the mud in the lot, through the parallel tanks, whose feeding is controlled by means of valves. Contrary to this patent, the treatment microplant subject matter of this invention possesses a continuous treatment system both of the residual water and the mud produced under a compact design, with the nitrogen elimination included.
U.S. Pat. No. 5,534,147 patent (1996) describes a residual water treatment system with separate tanks for residential houses, consisting of a conventional septic pit, an anaerobic recirculation tank, and an aerated unit for nitrification, packed with stones of granulometry less than 3/4". A recirculation current is established between the nitrifying tank and the conventional septic pit. The treatment plant effluent is obtained from the anaerobic tank for recirculation of the water that is discarded into an absorption well.
This plan, contrary to the residual water treatment microplant subject matter of this invention, produces an anaerobic effluent with a greater content of DQO and SST; besides, it has a design that is not compact. Denitrification is carried out in an anaerobic unit tending towards a complete mixture (recirculation tank) and in the septic pit, whose substrate-microorganism interaction is poor.